The overwhelming majority of high bromide tabular grain emulsions are {111} tabular grain emulsions. Usually all of the tabular grains in such emulsions have major faces lying in {111} crystal planes.
Although there are known performance advantages for high bromide {100} tabular grain emulsions, their use has been limited, since, compared to processes for preparing high bromide {111} tabular grain emulsions, their preparation processes are more difficult to control. Specifically, high bromide {100} tabular grains emerge as a result of grain ripening. Attempts to limit mean tabular grain edge length have resorted to terminating grain ripening while a significant proportion of smaller and non-tabular grains remain in the precipitation vessel. This does not represent an efficient use of silver or desirably high yields of high bromide {100} tabular grains. When grain ripening is prematurely terminated, the final emulsions resemble emulsions that are blends of {100} tabular grains and relatively fine grains. Thus, obtaining aim mean grain ECD's while also ripening to completion, thereby eliminating fine grain components, has not been realized.
The following patents have sought to prepare high bromide {100} tabular grain emulsions, although minimum definitional requirements (set out above) have frequently gone unrealized:
Bogg U.S. Pat. No. 5,063,951; PA1 Mignot U.S. Pat. No. 5,386,156; PA1 C. Precipitation procedures, paragraph (2), which identifies preferred procedures for controlling vAg and pH during precipitation (note particularly Chang U.S. Pat. No. 4,933,170, here incorporated by reference), and paragraph (3); PA1 D. Grain modifying conditions and adjustments, particularly paragraphs (3)-(5), which pertain to dopants; and PA1 E. Blends, layers and performance categories. A selection of conventional ripening agents are disclosed in paragraph (2).